Abstract: The present identifies collections of digital music and sound that effectively elicit particular emotional responses as a function of analytical features from the audio signal and information concerning the background and preferences of the subject. The invention can change emotional classifications along with variations in the audio signal over time. Interacting with a listener, the invention locates music with desired emotional characteristics from a central repository, assembles these into an effective and engaging “playlist” (sequence of songs), and plays the music files in the calculated order to the listener.